GRADUAL AND LONG-TERM DEVELOPMENT OF COMPLEX MARINE BENTHIC ECOSYSTEMS IN THE AFTERMATH OF THE END-PERMIAN EXTINCTION IN THE MOST STRATIGRAPHICALLY EXTENDED MIDDLE TRIASSIC REEF

The recovery of biodiverse reefs following the end-Permian extinction occurred during the Anisian (early Middle Triassic) when scleractinian corals, calcareous sponges, calcareous algae, and Tubiphytes combined to form the earliest biodiverse Mesozoic reefs. The long-standing interpretation of a geologically sudden (<< I Myr) occurrence of these more biodiverse reefs in the Western Tethys following stabilized environmental conditions implies that complex, integrated marine ecosystems can develop rapidly on geologic time scales. The limited stratigraphic range of Anisian Western Tethys reefs, however, makes it difficult to assess the pattern and tempo of reef ecosystem development. In this study, we investigated the pattern and timing of reef ecosystem recovery in the oldest-known and most stratigraphically extensive platform-margin reef of the Mesozoic Era—the Eastern Tethys Great Bank of Guizhou reef at Bianyang, south China. We integrated satellite imagery analysis, field mapping, biostratigraphy, and digital point counting to establish a stratigraphic framework for the reef and assess the pattern and timing of its development. Across 900 meters of reef stratigraphy, metrics of reef-builder recovery, including the proportion of biotic framework relative to cement, the volume of metazoan and algal framework, taxonomic richness, evenness, and body size, provide statistically significant evidence for a gradual, rather than sudden, recovery pattern lasting several million years. This gradual recovery substantially post-dates carbon cycle stabilization and increased ocean oxygenation, suggesting that recovery tempo was not merely a function of improved environmental conditions. Our findings suggest that complex, integrated marine ecosystems require several million years to develop, highlighting the importance of conserving modern marine ecosystems.