FEATURES OF DIAGENESIS AND GENESIS OF ATHINGENIC MINERALS IN BASALTIC SANDSTONES(UPPER PERMIAN SERIES)IN THE LANGDAI DISTRICT LIUZHI COUNTY GUIZHOU

The Upper permian Series in Langdai district of Liuzhi County, western Gui-zhou, is composed of cyclical sequences of basaltic lithic sandstones, siltssones, mudstones and coalbeds. An examination of sedimantary features reveals that all these layers were deposited in didal-swamp and subtidal enviroments. The description of diagenetic sequence for the basaltic lithic sandstone is given in the present paper, and the genesis of the authigenic minerals, i.e., Ti-Fe montmorillonite, Chlorite, ferrodolomite and ferrocalcite, in this sort of rock are discussed in detail on the basis of the authors study mean of various laboratory procedures such as thin section petrography, scanning electron microscopic analysis, electron prooe analysis, X-ray diffraction analysis,and carbon and oxygen isotope analysis for the carbonate, etc. . It is pointed out that: 1. The diagenetic sequence of basaltic lithic sandstones is Ti-Fe montmorillonite →c→ompaction→chloritization→dissolution→silicif ication, pyritization→ ferrodolomitization→ferrocalcitization→ferritzation, hemetitization. 2. The diagenetic stage and enviroment of basaltic lithic sandstones may be divided into. 1 )Shallow burial, early diagenetic stage, acid water enviroment; 2 ) Deepburial-mesodiagentic stage, weak base acid alkalinity water enviroment; 3 ) Nearsurface, late diagenetic, meteoric freshwater enviroment. 3. Geneses of these authingenic minerals are essentially controlled by the variety of combination patterns of the following factors: 1 ) composition and textur-e of the sandstones) 2 ) characteristics of assemblages of the sedimentary layers; 3 ) the reduction level of organic matter and its thermal maturation; 4 ) trasfor-mation and dehydration of clay minerals in the mudstones; 5 ) compection and 6 ) temperature and acidity or alkalinity of pore water