Kheirov M.B.

Processes of lithogenesis play an important role in the formation of geological peculiarities of oil and gas deposits.

Processes of lithogenesis of clays and clayey minerals start since the moment of entry into the sedimentation basin. This is due to the ion-exchange reactions between the clayey minerals and ions of the sea water, and a special role is played by ions Mg²⁺ and K⁺. They promote the formation of dior trioctahedral clayey minerals in the basin.

In the process of lithofication of sediments, depending on physical-chemical peculiarities and geochemical environment in the basin, there occurs the formation of various minerals by the authigenic way.

In the reduction geochemical medium there takes place the formation of the authigenic montmorillonite of the volcanic material.

In lagoons with high salinity of waters, there have been formed magnesian minerals of a chain-like structure (paligorskite, sepiolite).

During the subsidence of the sediments to large depth, there occur perceived katagenetic changes under the influence of increased values of thermobaric parameters. Rate of these processes in the lithofacial clays in not high due to a not intensive migration of ions. The swelling clayey minerals there may be preserved at depth more than 6–7 km. At rather high temperatures, the water may be removed out of them irreversably. But this does not mean the conversation of montmorillonite into chlorite or sericite. For this process the existence of elements necessary for the formation of chlorite or micas as well as conditions for their migration in a rock are required.