Pochodzenie chlorków w wodach górnego karbonu w świetle ilościowych obliczeń

Abstract

ORIGIN OF CHLORIDES IN THE UPPER CARBONIFEROUS WATERS, ACCORDING TO QUANTITATIVE CALCULATIONS

Summary

The purpose of the present work is to explain, on the basis of approximate quantitative calculations, the genesis of Cl’ ions found to occur in the Upper Carboniferous salt waters and brines, within the Upper Silesian Coal Basin. The previous authors related the origin of the brines from Carboniferous to the processes of leaching the salt deposits by atmospheric waters and to their infiltration into the substratum (R. Michael 1913, R. Rosłoński 1933). This opinion did not take into account the hydrodynamic possibility of an exchange of original Carboniferous waters for infiltration waters (J. Pałys 1966b, 1968). The Carboniferous formations are characterized here by a regular hydrochemical zonal arrangement that consists in an increase of water mineralization with depth (up to 150 g/l). In the northern and eastern parts of the Upper Silesian Coal Basin, the Coarboniferous strata are covered with an overburden series, mainly of carbonate Mesozoic deposits (Triassic, Jurassic), up to 200 m in thickness. In the southern and western parts, the Carboniferous formations are covered with clay of Miocene age (Tortonian), in the Carpathian foredeep - up to 800 m in thickness. In the westernmost part they occur, among others, in the fames of chemical deposits, with a hard salt series in the so-called Zawady graben. Their mass has been estimated to amount here about 1 milliard tons (R. Michael 1913). In the central part of the Upper Silesian Coal Basin the Carboniferous strata crop out (Fig. 1). The thickness of the Upper Carboniferous strata ranges from 700 m in the east, to 4000 m in the west. The following are parameters taken for calculations: the area of the basin - 3364 km², the total thickness of sandstones, the coefficients of water yield (0,01–0,05) and the mineralization of water taken from hydrochemical maps (5-150 g/l).
It has been established on the basis of the existing chemical analyses that in the group of waters characterized by the mineralization from 5 to 50 g/l, chloride occurs in 90%, whereas in the case of a higher mineralization, it is equal to 100%. The amount of Cl’ ions was calculated first, and then converted into the amount of NaCl salt. These calculations gave the total amount of chlorides, equal to about 3,57 milliard tons (Tabs. 1 and 2), this corresponding to 5,95 milliard tons of NaCl salt.

The calculated amount of NaCl salt, which occurs in the Upper Carboniferous waters, is sixfold greater than that found in the Zawady graben. Traces of leaching processes, which as a rule appear in the form of a characteristic residue, have not been encountered. In contrast to this, throughout the occurrence area the salt series are well isolated with a complex of impermeable clays, several hundred metres in thickness. Geological data, available at present, do not permit us to accept any considerable erosion that could have removed a salt complex sixfold greater than that preserved at present. A suggestion that any horizon, stratigraphically younger than the main horizon of the Thitonian evaporates, may have been eroded here must be ignored, since no equivalent of this kind have been found in the eastern part of the foredeep, where a complete section of the Tortonian deposits may be observed.Thus, the origin of most brines from the Carboniferous strata would be related to an earlier saliferous epoch, first in the history of the upper Silesian Coal Basin, i.e. to the Permian period (J. Bałys 1966b, 1968).