FAUNAL COMPOSITION OF MICROBIALITES FOLLOWING THE END-PERMIAN MASS EXTINCTION

After the end-Permian mass extinction, microbialites filled the ecological niche previously occupied by metazoan reefs. Within these post-extinction microbialites, small metazoans (usually <1 cm) are abundant; however, the variability in faunal composition and the role of metazoans in microbialite development are poorly understood, particularly with regard to variation both geographically and with water depth. Here we investigated the distribution and composition of post-extinction microbialites from China, Iran, Turkey, Armenia, Slovenia, and Hungary. Our results show that Neotethyan microbialites record a unique faunal association due to the presence of keratose sponges, whereas Chinese microbialites have a higher proportion of mollusks and echinoids. Microbialites with a high faunal diversity were also limited to settings above wave base; in contrast, microbialites that formed below the action of waves, but still within the photic zone, only contain low diversity microfaunas. In addition, the distribution of the faunal components within the microbial fabrics suggests that most of the metazoans were transported into the microbial mats, with the exception of the keratose sponges and some microconchids. Consequently, the action of waves is interpreted to have maintained atmosphere-seafloor gas exchange in shallow water settings, and to have transported enough molecular oxygen to the seafloor to support relatively diverse communities. Many of the identified metazoans from the post-extinction microbialites are not observed to have been living within a microbial mat. Likewise, the lifestyle of many of the taxa identified from the microbialites was not suited for, or even amenable to, life within a benthic microbial mat.