ELECTRON MICROSCOPE STUDY ON PEBBLE PHOSPHORITES OF MEISHUCUN SECTION, JINNING, YUNNAN PROVINCE

The microstructure and composition of phosphahic pebbles in phosphorites in Zhongyicun Member of Meishucun Section, Jinning, Yunnan Province have been carefully investigated by electron microscope. The investigations revealed that the composition of pebble phosphorites can be divided three different levels: pebble phosphorites consist of phosphatic pebbles and cement materials; phosphatic pebbles consist of phosphatic oolites, phosphatic microglobules and phosphatic amorphous aggregates are composed of phosphatic microcrystals and amorphous grains and non-phosphatic micrograins.The phosphatic amorphous grains and microcrystals are the most fundamental amd the smallest grains of phosphatic matters possibly observed under electron microscope. By the investigations of electron microscope, the followimg three stages of formation of pebble phosphorites are proposed: (1) Stage of formation of phosphatic amorphous grain aggregates and phosphatic microcrystals which were crystallized out from sea water; (2) Stage of formation of phosphatic pbbles; (3) Stage of formation of pebble phosphorites. The sedimentary environment of pebble phosphorites belongs to neritic deposit