Collapse-breccia as a sign of the pre-existing evaporites (Lower Riphean Satka suite, South Ural)

The presence of pre-existing evaporites in the carbonate unit is considered on example of the Lower Riphean Satka Suite. It is proved by the extensive development of the collapse breccia in the Karagay member of the Upper Satka subsuite. The difference of collapse-breccias from other sedimentary breccias is shown, and the mechanism of their formation due to the bio sulphate reduction processes is proposed. Diagenesis bacterial decomposition of sulphate led to a decrease in the concentration of the sulphates ion in the pore waters and the total dissolution of the gypsum and anhydrite with the formation of the collapse breccia horizons. A low level of oxygenation in the Mesopro-terozoic time supported a wide development of biosulphate reduction even in the photic zone of shallow lagoons under conditions of low hydrodynamic activity.