Fluor w wodach podziemnych wschodniej części Żuław Wiślanych

Abstract

Na podstawie analizy budowy geologicznej Żuław Wiślanych stwierdzono, że źródeł fluoru w wodach podziemnych można się doszukiwać w osadach cechsztynu i pstrego piaskowca. Z porównania mapy rozkładu stężeń fluoru z przebiegiem różnowiekowych uskoków wynika pewna zgodność między tymi zjawiskami. Na tym tle przedstawiono próbę odtworzenia paleohydrogeologii plejstocenu. Na podstawie analiz próbek wody udokumentowano poziomą strefowość hydrochemiczną wód słodkich i powiązano ją ze współczesnymi ruchami pionowymi skorupy ziemskiej.

FLUORINE IN GROUNDWATER IN EASTERN ZULAWY WI8LANE REGION

The unpublished records compiled till 1984 show concentrations of fluorine up to 3.2 mg/dm³ in groundwaters from rocks of the Cretaceous. Tertiary and Quaternary age in eastern part of the Zuławy Wiślane region, east of the Vistula River. Simultaneous tests made in 1984 showed that the concentrations already raised up to 3.5 mg/dm3 (Fig. 2).

The paper presents brief discussion of distribution and conditions of migration of fluorine in the Earth crust and, subsequently, presence of that element in Żuławy at the background of geological structure of this region. With reference to the record of high concentrations of that element in the Zechstein of the Peribaltic Syneclize, presented in the papers by H. Ważny, the Authors put forward a conception of migration routes of fluorine towards the Earth surface along with groundwater. Figure 1 shows a scheme of geological structure of the studied region.

The analysis of water samples taken simultaneously in 32 wells made it possible to trace horizontal hydrochemical zonality in fresh waters of the studied region. Hydrogen-carbonate-calcium waters predominate in the Elbląg area, and hydrogen-carbonate-sodium - in the Malbork area, whereas chlorine-sodium ones remain known from a single well in northern part of the Żuławy region. Mineralization of the latter is over 1.5 g/dm³. The above differentiation is possibly due to different hydrodynamic conditions. Chemical composition indicates young (Holocene) age of waters from the Elbląg area whereas those from the Malbork area may of the Pleistocene age.

The analysis of variability in chemical composition of waters and concentration of fluorine in relation to the course of faults in Precambrian, Paleozoic, and Mesozoic rock sequences showed that fluorine migrates along fractures cutting Mesozoic rocks. The fractures originated or became rejuvenated in times .of transgressions and regressions of Scandinavian icesheets.

The available data appear insufficient for unequivocal solution of the question whether fluorine migrates at present from the Zechstein (or Triassic}or it was supplied to Cretaceous aquifer waters in the Pleistocene and at present we are merely dealing with its dilution and migration along with water flow. The conditions from times of transgressions of icesheets, i.e. times of large·amplitude crustal movements and squeezing water from large depths upwards, may be interpreted as most advantageous for migration of fluorine.