The Middle Triassic environstratigraphy of central-south Guizhou, southwest China

Environstratigraphy is proposed to produce a direct stratigraphic correlation for the Middle Triassic sequences of entirely different lithologic and palaeontologic compositions in various palaeogeographic environmental gradients (facies) of southern Guizhou. As environstratigraphy is based on environmental analysis, various indicators of environments can be used to complete the environstratigraphic sequence. The Middle Triassic environstratigraphic sequence in the terrigenous clastic basin of southern Guizhou is established mainly by the study of sedimentology and community ecology. Microfacies analysis is very useful for the environmental reconstruction in carbonate sedimentary areas, for example the carbonate platform and carbonate buildup in front of a platform. The method of geochemical facies analysis has been developed for a comprehensive evaluation of relative environmental changes, and it is very suitable for environstratigraphic study. Environstratigraphic correlation is based on the regional significant environmental events and their effects at different palaeogeographic gradients. The alternations of tectonic environments indicated by sedimentation are of great importance for the direct correlation of the events at different environmental gradients. The six correlation lines divide the Middle Triassic development of the basin into five intervals, which exactly express the periodicity of sedimentation in various areas and the evolutionary process of tectonic and palaeogeographic patterns.