High Energy Stromatolites-Associated Sediments from Middle Triassic(guizhou, China)

The so‐called Permian-Triassic mass extinction was followed by a prolonged period of ecological recovery that lasted until the Middle Triassic. The stromatolites-associated sediments from the Pazichang area of Guanling (Guizhou, China) seem to be important components of the puzzle and have not been extensively studied to date. This study used five petrological methods, including OM, CL, μ-XRF, SEM, and EDS testing. The results showed that significant microbial skeletal mixed carbonates were formed in the high-energy environment at the edge of shallow marine carbonate platforms during the Middle Triassic Anisian period. In situ coral skeletons are implanted in biofilm channels formed by Tubiphytes and microbial activity, typically enveloped by Tubiphytes and calcareous microorganisms. The mutually beneficial relationship between microorganisms and Tubiphytes allows these organisms to fill the ecological niche cleared after the Permian-Triassic crisis, meaning that these microbial metazoan communities remained dominant until the Middle Triassic. In the microbial skeletal mixed carbonates, stromatolites are products of biological encrustation dominated by Solenoporaceans and cyanobacterial communities of the genera Cayeuxia, Zonotrichites, Renalcis, and Bevocastria. Among these, Cayeuxia can be compared to modern Rivularia, possessing broad environmental adaptability, surviving under high-energy conditions in the study area. The development of this complex may reflect significant changes in the ancient environment, possibly due to the interaction between high seawater Mg2+/Ca2+ molar ratios and cyanobacterial mat evolution within the mixed carbonates. Stromatolites in the Ladinian period contain few fossils, with dark laminae developing a window-pane-like structure parallel to the laminae. Except for the effects of microscopically unidentifiable microbial functional groups, identifiable iron-rich growth layers indicate the presence of sulfate-reducing bacteria, which induced microbial formation in the laminae and contributed to stromatolite development. Thus, Middle Triassic stromatolites differ from post-extinction opportunistic and “anachronistic facies”; they do not necessarily indicate anoxic or oxygenated conditions. Their environmental setting is much more complex than previously thought.