HABITAT SELECTIVITY OF BENTHIC COMMUNITIES IN MICROBIAL REEF ECOSYSTEMS FOLLOWING THE LATE PERMIAN MASS EXTINCTION EVENT

Oxygenic photosynthesis (by cyanobacteria) in thrombolite and stromatolite habitats can provide an oxygenated refuge for invertebrates. The importance of this oxygenated refugia is becoming increasingly recognized throughout the Phanerozoic. Based on the findings of oxygen-dependent invertebrates in microbial habitats in the latest Permian mass extinction aftermath, it has also been proposed that the microbial mats, which flourished in the extinction aftermath, provided an oxygenated refuge in otherwise anoxic settings. Here we investigated the distribution of 33,339 bioclasts from 83 samples from the Great Bank of Guizhou, an isolated shallow marine carbonate platform in south China that spans the Permian-Triassic transition, representing thrombolite, stromatolite, and non-microbial habitats. The investigated habitats are all interpreted to have been deposited above wave base. The stromatolite habitats were the least diverse, but thrombolite habitats also recorded significantly lower diversities when compared to the non-microbial habitats. We also found that bioclasts within the thrombolite and stromatolite habitats were transported and concentrated in the non-microbial fabrics, i.e. cavities around the microbial framework. Therefore, many of the identified metazoans from the post-extinction microbialites are not observed to have been living within a microbial mat. Furthermore, the lifestyle of many of the taxa identified from the microbial-metazoan reefs is not suited or amenable to life within a benthic microbial mat. The high-diversity of oxygen dependent metazoans on the Great Bank of Guizhou suggests that the benthic ecosystem was also oxygenated in non-microbial habitats.