Clay minerals and their palaeoclimatic indicators in the Mawo karst basin in Weining, Guizhou

The present paper deals with the evolution of the palaeoclimatic conditions of the Mawo karst basin in Weining, Guizhou on the basis of composition, content, crystallinity index, chemical index and relative content of the clay minerals by using the X-ray diffraction analysis. The clay minerals in the study area are composed dominantly of mixed illite-montmorillonite layers (30%-75%) and chlorite (10%-45%), and subordinately of gaolinite (5%-20%) and illite (10%) with no montmorillonite, and derived from the weathering of the surrounding bedrocks. Four stages are recognized for the evolution of the palaeoclimatic conditions in the study area, including three major climatic cycles and several minor climatic cycles.