Composition, morphology, and origin of phosphate pellets: Evidence from phosphorites of the Lesser Karatau

The global Vendian-Cambrian epoch of phosphate accumulation is marked by the virtually synchronous appearance of giant sedimentary basins, where the largest phosphate-bearing provinces were formed in a relatively short time span. The paper is devoted to one of the main problems in phosphate geology, namely the origin of phosphate pellets. They are observed as microscopic particles in the stratified microgranular phosphorites formed during the Vendian-Cambrian epoch. Different forms of pellets from the productive formation of the Lesser Karatau were studied with the scanning electron microscope. The morphogenetic comparison of phosphate particles and microbiota found in the Vendian-Cambrian or older rocks was carried out. The distribution of major chemical elements in different pellets was studied for the first time. Based on the results obtained, regularities of the vertical and lateral distribution of phosphate pellets in the Lesser Karatau and the issue of their origin is discussed.