Carbonate nodules have been examined – those forming numerous lenticular chains of diverse lengths at each hypsometric level in the Middle Jurassic deposites. Contrary to the current view of the siderite composition of the nodules, dominant calcite development is proved, with siderite and clay matter involved. The material composition of the nodules is characterized by substantial variations of the component concentrations. Inherent peculiarities of the mineral and of the chemical compositions have been revealed in each suite, alongside with specific textures.
