Аннотация:An opinion has been substantiated that the rocks of ferruginous-siliceous-carbonate formation of the Bug and Golovanev suture zone are endogenous. Their appearance is synchronous with the appearance of rocks of the Gadantsev suite of the Krivoy Rog–Kremenchug zone. Peculiarities of this formation and of enclosing strata of the Bug series can be explained by behavior of the geodynamic process, sharp change of composition of deep fluid which accompanied differentiation of asthenospheric melt as well as crystallization under conditions of granulite metamorphism facies. Specific composition of rocks of this formation depends on mixing of the residual water chloride-potassium and deep carbonate-fluoride-sodium fluids.