Early Triassic stromatolites from the Xingyi area, Guizhou Province, southwest China: geobiological features and environmental implications

• Autores: Shilei Liu, Jian Wang, Fuguang Yin, Tao Xie, Shixue Hu, Xiaofeng Guan, Qiyue Zhang, Changyong Zhou, Wanhua Cheng, Jinsha Xu
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 32, Nº. 3, 2017, págs. 261-277
• Idioma: inglés
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• Resumen

  • An Early Triassic stromatolitic deposit is documented in the Dienerian succession of the Lower Triassic Feixianguan Formation in the Xingyi area, Guizhou, southwest China. Five types of constructional microbial forms at various scales were observed. (1) Typical stratified columnar structures, up to 25 cm in height, with crinkled laminae. Dark-coloured laminae, 1 mm thick, are composed of upright filamentous tubes, average diameter 5 µm, showing a vertical growth fabric. (2) Prostrate filaments showing strong fluorescence, in sharp contrast to the micritic cement. (3) Coccoid-like spheroids and algal filaments are also common in stromatolitic laminae. These resemble present-day cyanobacteria, and thus may represent fossilized cyanobacteria. (4) Smaller bacilli resembling Pelodictyon are very common in the stromatolitic laminae. (5) Framboidal pyrite is also abundant and probably indicates biological involvement in stromatolite formation. Two major microbial functional groups, oxygenic phototrophs represented by lithified cyanobacteria and probable sulfate-reducing bacteria represented by framboidal pyrite, were present during stromatolite growth. Another possible microbial functional group, anoxygenic phototrophs represented by lithified remains resembling Pelodictyon clathratiforme, may be present in the Xingyi stromatolites, and were involved in stromatolite formation by capturing or adhering microcrystalline particles. All of these features demonstrate that the Early Triassic stromatolites are biogenic. The occurrence of the Xingyi stromatolites, corresponding to a second episode of microbial growth during the Early Triassic, reveals that post-extinction microbialites were widespread in the Dienerian. These Early Triassic stromatolites indicate that a microbial bloom took place in the aftermath of the Permian–Triassic mass extinction.