Caves in slightly karstic rocks of Altai-Sayan mountain region: formation mechanism and Morphology

In addition to numerous underground cavities associated with the processes of dissolution of carbonate rocks, within the Altai-Sayan mountain region there are a number of caves developed in non-karstic and slightly karstic rocks. Among them, the caves of the conglomerate Narva rock mass of the Badzheiskii massif (Eastern Sayan, Manskii trough) stand out due to their size. The most outstanding caves here are Big Oreshnaya, Dudinskaya and Badzheiskaya, the length is more than 50 km, 35 km and 10 km respectively. The limestones of the middle Altai mountains are often in contact with effusive and intrusive rocks and are altered within the contact zones of metamorphism to dense marbleized rocks, which makes it impossible for karst processes to occur. Nevertheless, in the marbled Lower Cambrian limestones of the Kayanchinskaya suite of the Altai Mountains, large Altaiskaya and Kek-Tash caves with a total length of 4.7 and 3.2 km, respectively, are developed. Detailed mapping of the caves was carried out, which showed their close spatial connection with the systems of the latest faults. In caves along fault zones, signs of widespread argillization were found (changes in the original substance by hydrothermal processes and its replacement by newly formed clayey minerals). The mechanism we propose for the formation of caves in non-karstic and slightly karstic rocks comes down to the removal by groundwater of a substrate argillized by hydrothermal processes along fault zones without significant participation of dissolution (karst processes). This makes this mechanism some similar to the well-known process of “clay karst” associated with suffusion in clayey rocks. The difference comes down to the development of the forms and processes we studied in argillicized fault zones, and not in clayey strata.