Hydrogeodynamic processes in carbonate rocks. Part II. Karst and its influence on geological environment

Abstract

Formulation of the problem. Chemical activity of groundwater in the natural geological environment is caused by chemical reactions in a complex physical-chemical system "rock-water-gas". Leaching and dissolution play the leading role in carbonate rocks. These processes can best be described by the laws of chemical thermodynamics, which can justify the existence of the relationship between the reactions themselves, and determine the amount of energy consumed by them. This enables to establish not only direction of physical and chemical transformations but also their results in certain geological, hydrogeological and geochemical conditions. The consequences of chemical activity of groundwater can be the following: 1) physical and chemical destruction and formation of minerals and rocks; 2) migration and concentration of chemical elements and their compounds in solutions; 3) formation of groundwater chemical composition.Presentation of main material. Sorption and ion exchange processes play an important role in carbonate water systems. Sorption is the process of selective absorption of liquid and gaseous substances by solid phase and contributes to penetration of various chemical composition in water solutions into rocks.Depending on the depth of karst cavities, karst is divided into young and ancient according to the time of formation. According to the development of covering sediments on the rocks, karst is distinguished by open (without soil-vegetation cover) and closed (blocked by younger formations). Formation and development of closed karst is almost exclusively due to the action of groundwater located in the aquifer, in the rocks where there is karst formation. Instead, open karst is formed with the participation of both underground and surface infiltration waters.Anthropogenic (man-made) factors play an important role in geochemical processes in the "rock-water" system in urban and industrial conditions. They can manifest both through physical and chemical destruction of rocks, on which buildings and structures were constructed, and due to artificial groundwater contamination up to the change of their geochemical type.Conclusions. Karst is a geodynamic consequence of geological activity of groundwater, manifested in dissolution and removal of rocks with the formation of a liquid runoff. For the karst to develop, the following basic conditions are required: a) physical - significant thickness of carbonate rocks and low groundwater level; b) chemical - alkalinity of underground waters of bicarbonate-sodium composition and presence of soluble and free carbon dioxide in them.Hydrogeological peculiarities of karst development on the territory of research are based on the role of cracks and cavities in the filtration of groundwater of different formations and ascending unloading of aggressive to carbonates water from deep horizons and carbon dioxide, as well as unfavorable physical-chemical conditions of marl and chalk rocks dissolution.