Origin of Lower Triassic microbialites in mixed carbonate-siliciclastic successions: Ichnology, applied stratigraphy, and the end-Permian mass extinction

Results show that the highest trace fossil diversities are found in lower shoreface environments, while offshore environments contain the lowest diversity. Strata deposited in the offshore transition, separating lower shoreface and offshore environments, contain moderate diversity trace fossil assemblages. Microbialites, in the form of either stromatolites or wrinkle structures, appear to emerge only following transgression, and are commonly found across and following marine flooding surfaces. Wrinkle structures appear to have formed as low-oxygen waters encroached upon nearshore settings, suppressing bioturbation and allowing for microbial mat development. Stromatolites likely formed due to the upwelling of anoxic alkaline waters during transgression, which may have generated a firm substrate for colonization, as well as fostering cementation of the microbialite. While most studies examining the aftermath of the end-Permian mass extinction focus on either carbonate- or siliciclastic-dominated settings, this study reports the environmental distribution of microbialites in both carbonate and siliciclastic facies, and unites them into a single depositional model that accounts for stratigraphic distribution, relation to trace fossils, and the unique environmental conditions present during the aftermath of the end-Permian mass extinction.