Abstract:

Aiming at understanding the Middle-Late Triassic drowning of the Yangtze carbonate platform, this paper analyzes
the microfacies of the Middle-Upper Triassic Zhuganpo Formation in Zhenfeng area, Southwestern Guizhou and discusses its
depositional environment evolution. Using standard microfacies type methods of Flügel, nine microfacies including laminated
bindstone, peloidal packstone, micritic limestone, bioclastic wackestone, encrinite packstone, intraclastic-ooid-bioclastic
grainstone, lump-bioclastic wackestone, bioclastic wackestone-pelagic, and micritic limestone-pelagic are recognized. The ordered
combination and stratigraphic distribution of these 9 microfacies show that they were formed during the rapid transition from tidal
flat to carbonate platform margin environments, and the prolonged deep shelf and basin environments. The analysis of sea-level
changes of the Zhuganpo Formation indicates that they were different from the main part of Yangtze Platform, but their third-order
cycles and second-order cycles were briefly concordant with global sea-level changes.

Key words: microfacies, depositional environment evolution, Zhuganpo Formation, Southwestern Guizhou