The Late Devonian and Early Carboniferous encompassed the decline and recovery of global reef ecosystems during a time of climatic and sea level fluctuation. Frasnian stromatoporoid-coral-microbial reef communities gave way to Famennian microbe-dominated communities. Deep-water Waulsortian mounds characterise parts of the Early Carboniferous, but a range of Visean skeletal and microbial reefs and bioherms represent a period of "recovery" of shallow marine reef communities. Comparison of reefs in this age from four regions shows that reef development is significantly influenced by tectono-stratigraphic settings.
Devonian reef complexes in the Canning Basin, Western Australia grew in an intracratonic basin, representing a classic 'Great Barrier Reef' model. Devonian reef complexes and extensive Early Carboniferous carbonate shelves in South China developed in a pericratonic basin at a passive continental margin, depicting a successive and stable mid-Palaeozoic platform setting. Early Carboniferous reefs in eastern Australia and Japan developed in a forearc basin and on seamounts, respectively.
New sections on Devonian platform margins and reef edges in Guilin, South China were compared with those in the Canning Basin. Reef subfacies, reef complex architecture, temporal reef builder associations, and platform cyclicity in the two regions are similar. However, carbonate complexes are more widespread in South China, and have a much thicker sequence. Most Canning Basin reefs grew directly on Precambrian crystalline basement, but in South China, carbonate complexes developed on earlier Devonian siliciclastic sediments. Pre-Frasnian reef facies in South China have more skeletal frameworks than the Canning Basin reefs, and Famennian shoaling margins are more common and more diverse in South China. More platform margin types were recognized in the Canning Basin, possibly owing to relatively less deformation.
Studies on the Visean Cannindah reef limestone near Monto; Queensland revealed five primary reef subfacies. The reefs developed on shallow-water oolitic-crinoidal banks with thrombolites contributing to initial reef stabilization. Colonial rugose and tabulate corals formed bafflestone and framestone on the thrombolites. Subsequently, calcimicrobes and microencrusters enhanced reef framework. Up section, reefs were formed by Parachaetetes, sponges and microbes. Cannindah reefs are the largest Lower Carboniferous reefs in eastern Australia (more than 146 m thick) and contain abundant reef-building microbes (Renalcis, Palaeomicrocodium, and Girvanella), microencrusters, and algae. As in other Lower Carboniferous reefs in eastern Australia, sponges, thrombolites, fasciculate rugose corals, and syringoporoid corals are significant in reef building. Cannindah reefs differ from Lower Carboniferous reefs in Akiyoshi limestones, southwest Japan and Tianlin, South China in reef builders, textures, facies, and palaeogeographic settings.
Similarities and differences between Devonian reefs in the Canning Basin and South China were primarily controlled by the intracratonic faults and on-shore fringing tectono-sfratigraphy in the Canning Basin versus the pericratonic faults and platform-depression- dominated tectono-stratigraphy in South China. Basically, basin types associated with different tectonic configurations controlled stratigraphic framework, and, in turn, affected the distribution and growth of carbonate platforms. Basement-involved faults controlled reef development and occurrence in both regions. In South China, NE-SW trending faults, with predominantly strike-slip displacements, superposed by NW-SE trending faults, resulted in unique platform-to-intraplatform depressions, which controlled Devonian reefs. The more complex fault system in South China led to more fault-controlled highs for reef formation. Also, different tectonic evolution resulted in a longer reef history in South China.
Coral-sponge-microbial patch reefs are common in the limited limestones in the forearc basins of eastern Australia; rare microbialite-coral-bryozoan patch reefs occur in the passive marginal basin of South China; and coral patch reefs rest on top of seamounts now accreted to Japan. Differences in reefs were caused by local palaeoenvironments, nutrition supply, and terrigenous sedhnent influx associated with the different Early Carboniferous tectono-stratigraphic settings in Australia, South China, and Japan. The formation of large Cannindah reefs may represent (1) very abundant microbes, microbialite and microencrusters involved in reef formation; (2) a relatively clean environment without terrigenous clastic material; and (3) a high energy, near wave base, setting. Extensive tidal and restricted platform facies with a large terrigenous influx in the Canning Basin may have excluded Early Carboniferous reef growth there. Rare Early Carboniferous reefs in South China may reflect (1) early reef recovery in forearc basins at active convergent margins following Late Devonian bioevents; (2) glacial events affecting passive continental margins; and (3) the lack of distinct fault-generated topographic highs.