Metamorphism of natural waters in the crust of weathering—3

Abstract

Abstract ∗ The problem of the origin, occurrence, and distribution of soluble salts and the formation of chloride brines in the crust of weathering are treated in the present paper as a process caused chiefly by the dynamics of natural waters and the mobility of the chemical constituents dissolved in water. The hydraulic gradients and velocity of underground flow, the intensity of the water exchange with the earth's surface, the relation of the water-bearing bed to water (e.g., intensive flush, hampered flush, salt accumulation), the subsurface drainage conditions, the duration of time of the contact of water with the geological formations along with the chemical composition of rock material and the water which occurs in them and the structural features of the area, are considered as the chief factors governing the salinity variation of subterranean waters. Nearly ten thousand chemical analyses of natural waters, including fresh water and brines, subterranean waters from the numerous artesian basins, oilfield areas, geysers, mud volcanoes, from various sedimentary formations, metamorphic and igneous rocks from the different parts of the globe, have been classified, tabulated and plotted and considered in this paper. The relationship between the types of the products of weathering and the major geochemical types of subterranean waters has been found and used for the classification of water. The variation in salinity of subterranean waters with the change of the hydraulic gradients, with depth of water, with the distance from the outcrops and with the distance from the sea, have been illustrated by numerous data. The principles of the distribution of subterranean waters of the different hydrochemical facies (low saline facies, transitional facies, high saline facies) in the crust of weathering in relation to the hydrodynamic cones, salinity concentration and geological environment (structures, relation to water, depth) are indicated. The application of the integral frequency curves of the chemical composition of the different types of subterranean waters associated with oil-pools has been demonstrated for practical use in the search for oil. Ionic ratios Cl ′ Mg .. ; SO ′' 4 Cl ′ ; Ca .. Mg .. ; Na . + K . Na . + K . + Ca .. + Mg .. in subterranean waters and in oceanic water have been treated as the objective criterions showing the origin of highly-concentrated chloride brines. The metamorphism of natural waters in the crust of weathering is considered as proceeding either in the normal course (bicarbonate waters → bicarbonate-chloride waters → chloride-bicarbonate waters → chloride-sulphate or sulphate-chloride waters → sulphate waters → chloride waters), or in the reverse course, which is, for the major geochemical groups of water, as follows: bicarbonate sulphate chloride ← ← waters waters waters This process is formulated in this paper as the cycle of metumorphism of natural waters.