THE MIDDLE TRIASSIC ENVIRONSTRATIGRAPHY OF CENTRAL-SOUTH GUIZHOU, SOUTHWEST CHINA

Environstratigraphy is proposed to produce a direct stratigraphic corr elation for the Middle Triassic sequences of entirely different lithol ogic and palaeontologic compositions in various palaeogeographic envir onmental gradients (facies) of southern Guizhou. As environstratigraph y is based an environmental analysis, various indicators of environmen ts can be used to complete the environstratigraphic sequence. The Midd le Triassic environstratigraphic sequence in the terrigenous elastic b asin of southern Guizhou is established mainly by the study of sedimen tology and community ecology. Microfacies analysis is very useful for the environmental reconstruction in carbonate sedimentary areas, for e xample the carbonate platform and carbonate buildup in front of a plat form. 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 alterna tions of tectonic environments indicated by sedimentation are of great importance for the direct correlation of the events at different envi ronmental gradients. The six correlation lines divide the Middle Trias sic development of the basin into five intervals, which exactly expres s the periodicity of sedimentation in various areas and the evolutiona ry process of tectonic and palaeogeographic patterns. (C) 1998 Elsevie r Science B.V. All rights reserved.