Abstract:

 Through the field measurement and microscopic observation, 10 microfacies types have been recognized from the layers of 78 to 91 in the Middle Triassic Upper Member of Guanling Formation, where the Panxian Fauna occurs. The fossilbearing beds also include their overlying layer of 92 and underlying layer of 77. The division and analysis of microfacies is based on particle types, the content contrast of particles and matrix, depositional fabric, fossil assemblages and taphonomic types. By comprehensive microfacies analyses, it is shown that the sedimentary facies of the fossilbearing beds change upward from opencarbonate platform to restricted carbonate platform and to tidal channel. The presence and abundance of pyrite indicates that the paleoenvironment was somewhat anoxic, which helped the exquisite preservation of Panxian Fauna. The grain size and content show that the hydrodynamic condition changed from weak to strong，then weak again upward to the fossilbearing beds. It is consistent with the changes of the body size of the marine reptiles. According to the analysis of microfacies types and petrographic characteristics, the Panxian Fauna probably lived in a restricted carbonate platform.

Key words: microfacies analysis, palaeoenvironment, Panxian Fauna, Middle Triassic, Guizhou