Mechanisms of the Formation of Sodium Bicarbonate Groundwaters in the Southeast of West Siberia
статья в журнале
(ИНГГ СО РАН)
дата публикации: 2021
The research data are presented on the chemical and isotope composition of sodium bicarbonate groundwaters in the southeast of West Siberia. It is shown that the studied waters occur ubiquitously within MesozoicCenozoic sedimentary deposits at a depth roughly from 50300 m to 1.02.3 km. Various geochemical characteristics and conditions of occurrence made it possible to distinguish five types of waters: (I)яfresh, (II) brackish, (III) high-alkaline low-saline, (IV) coal-deposit saline, and (V) carbonated waters. Types I and II are characterized by regional occurrence and a quite typical chemical composition. Types IIIV have specific compositions and occur locally throughout the region. The genesis of all types of bicarbonate waters was determined as infiltration based on isotope data (18O, D, and 13'). Type IV is characterized by a positive oxygen shift and the carbon source is biogenic, except for type V. Calculations of equilibrium in the water-host minerals system showed that all bicarbonate waters were nonequilibrium for a number of primary aluminosilicate minerals and equilibrium for a wide variety of carbonates and clays. It was found that the amount of water-equilibrium minerals increased from type I to type IV with increasing water total dissolved solids (TDS) and pH values. The studies identified the governing characteristics of the formation of secondary minerals and hence of bicarbonate waters, including the main (pH value, Si, Ca, HCO3, and Al) and additional parameters of the medium (organic matter and gases). The same mechanism for all types of bicarbonate waters was determined: dissolution of water-nonequilibrium aluminosilicate minerals of sedimentary deposits and simultaneous precipitation of carbonates. The diversity of manifestations of bicarbonate waters is related to different interaction times in the waterrock system (types I and II), even during the bicarbonate stage, as well as additional overprinting of environmental features, i.e., the occurrence of supplementary sources of CO2 and organic matter for types IV and V, respectively, or their absence for type III. The presented formation schemes for different types of bicarbonate waters were also confirmed by the data of 18O and 13' isotope studies.
первоисточник: Geochemistry International