Lithology of karst deposits of the uppen visean section of the Zalesskaya area (north-western part of the Orenburg region, Russia)

Poorly studied deposits of the Upper Visean section of the south-east of the Orenburg region are one of the promising objects of geological exploration. A powerful stratum of dolomite breccias is described in one of the wells of the Zalesovo area in the lower part of the undifferentiated the Venev, Mikhaylov and Aleksino strata of the Visean section. The section is composed of secondary dolomites with relics of primary textures and structures. Dolomitization complicates interpreting the genesis of deposits and conduct detailed sedimentological studies. Lithotypes of rocks are identified based on the analysis of a set of data from lithological and mineralogical studies. Lithotypes: 1) secondary dolomites with relics of primary textures, 2) dolomite breccia with clay-carbonate cement, 3) secondary breccia dolomites with relics of primary textures, 4) dolomite breccia. A detailed lithological description of the lithotypes is given. The features of their formation are determined. Reservoir properties of rocks are analyzed. It has been established that the sediment complex encountered in the section of the Uppen Visean section of the Zalesovo area are the result of different stages of karst formation and following transformation of rocks. Reservoir properties of rocks depend on the development of post-sedimentation transformations. Karst processes and their products require further study at the regional level and consideration when conducting geological exploration on productive reservoirs of the Uppen Visean section.